The present invention is related to a grid quality judging apparatus, a grid quality judging method, and a grid quality judging program for judging the quality of a scattered ray removing grid or for generating quality data that represents the quality of the scattered ray removing grid, which is utilized in cases that radiation images are obtained, that removes the influence of scattered rays scattered by a subject.
When obtaining a radiation image of a subject formed by radiation which has passed through the subject, scattered rays are generated within the subject, particularly when the thickness of a subject is great. Conventionally, there is a problem that these scattered rays decrease the contrast of the obtained radiation image. For this reason, there are cases in which a scattered ray removing grid (hereinafter, simply referred to as “grid”) is provided between the subject and a radiation detector for detecting radiation to obtain a radiation image such that the scattered rays are not irradiated onto the radiation detector when performing imaging. If imaging is performed employing the grid, radiation which is scattered by the subject becomes less likely to be irradiated onto the radiation detector, and thereby the contrast of an obtained radiation image can be improved.
A grid is constituted by alternately arranging lead or the like, which does not transmit radiation, and an interspace material such as aluminum, fiber, etc., which readily transmits radiation, at a fine grid density of approximately 4 lines/mm, for example. For this reason, periodic patterns caused by the grid, such as periodic stripes and moire patterns, are generated within radiation images when the grid is employed to perform imaging, resulting in the radiation images becoming difficult to view. Note that a moire pattern is a fine periodic pattern which is generated in the case that the grid density is greater than the Nyquist frequency of a radiation image.
For this reason, various techniques have been proposed to obtain images, of which observation is facilitated, in which periodic patterns are reduced by administering filtering processes to remove the frequency components of periodic patterns (refer to Japanese Unexamined Patent Publication No. 2002-152467).
There are cases in which there are fluctuations in the grid density of grids, which is the number of stripes per unit length, due to manufacturing error and deterioration over time. For this reason, a technique has been proposed, in which interval defects of grids are detected by performing imaging while varying the orientation of the grids, then detecting the interval defects based on the signal strengths of grid images obtained by the imaging operations (refer to Japanese Unexamined Patent Publication No. S61(1986)-133848).